1. Field of the Invention
The invention relates to a continuous flow steam generator having a double-flue construction, with a combustion chamber rear wall of a first vertical flue, the rear wall being inclined inwards relative to the combustion chamber in an upper part region thereof and thereby forming with the bottom of an adjoining horizontal gas flue a xe2x80x9cnosexe2x80x9d which projects into the combustion chamber. Such a nose in the upper part of the combustion chamber rear wall at the transition into the horizontal gas flue improves the conduction of the flue gas.
A continuous flow steam generator of a double-flue construction having such a xe2x80x9cnosexe2x80x9d is illustrated in FIG. 1 of U.S. Pat. No. 3,174,464. Some of the steam generator tubes in the lower part of the combustion chamber rear wall are guided uninclined up to a supporting structure outside the heating gas conduction and thus serve as a support for the combustion chamber rear wall which has the xe2x80x9cnosexe2x80x9d.
A separate partial heating surface with an inlet header and an outlet header has usually been employed for suspending the combustion chamber rear wall, in order to avoid stability problems and possibly resulting tube fractures in the supporting tubes through which mainly wet steam flows. This suspension structure is highly complicated. Another disadvantage is usually the temperature difference between the supporting tubes, which are combined to form a separate partial heating surface, and the combustion chamber side walls, when the flow does not pass through these heating surfaces in parallel, but, as is customary, in succession. Above all, when a still hot continuous flow steam generator is being filled with colder feed water before the burners are ignited, considerable temperature differences occur between the supporting tubes of the combustion chamber rear wall and the combustion chamber side walls. These temperature differences may damage the tubes as a consequence of inadmissibly high thermal stresses.
It is accordingly an object of the invention to provide a continuous flow steam generator which overcomes the above-mentioned disadvantages of the heretofore-known steam generators of this general type. In particular it is an object to provide a cost-effective and operationally reliable configuration for supporting or suspending a combustion chamber rear wall, or, in general terms, a cost-effective and operationally reliable way of fixing the combustion chamber rear wall in a supporting structure above a pressure part of the steam generator
With the foregoing and other objects in view there is provided, in accordance with the invention, a continuous flow steam generator of a double-flue construction, including:
a horizontal gas flue having a bottom;
a vertical gas flue adjoining the horizontal gas flue and having a combustion chamber and an evaporator heating surface forming a combustion chamber rear wall, the combustion chamber rear wall having a lower part region, an upper part region, and a side facing away from the combustion chamber;
the combustion chamber rear wall being essentially vertically oriented in the lower part region and being directed approximately toward the horizontal gas flue, the vertical gas flue having an ascending conduction of a fuel gas and being connected, with respect to a direction of the conduction of the fuel gas, in series with the horizontal gas flue;
the combustion chamber rear wall having steam generator tubes ascending next to one another, being joined to one another in a gas-tight manner, and being connected in parallel for a flow medium to flow through the steam generator tubes, the steam generator tubes including a plurality of first steam generator tubes and a plurality of second steam generator tubes;
the plurality of first steam generator tubes being inclined inward in the upper part region of the combustion chamber rear wall, toward the combustion chamber, and forming, together with the bottom of the horizontal gas flue, a nose projecting into the combustion chamber;
an approximately horizontally extending balancing header disposed on the side of the combustion chamber rear wall facing away from the combustion chamber;
inlet tubes and respective outlet tubes disposed above the inlet tubes, connecting respective ones of the plurality of first steam generator tubes to the balancing header, the balancing header flow-connecting the plurality of first steam generator tubes beneath the upper part region;
the plurality of second steam generator tubes extending as a support of the combustion chamber rear wall in the lower part region uninclined upwards to a supporting structure located outside the conduction of the fuel gas;
pressure-balancing tubes respectively flow-connecting the plurality of second steam generator tubes to the balancing header; and
separating discs respectively provided in the plurality of first steam generator tubes between the inlet tubes and the outlet tubes.
In accordance with another feature of the invention, the balancing header has a crown region. The inlet tubes open into the crown region and the outlet tubes are led away from the crown region.
In accordance with yet another feature of the invention, a separate outlet tube is led out of the balancing header in a region of one of the plurality of second steam generator tubes. The separate outlet tube is led inclined into the upper part region of the combustion chamber rear wall and is parallel with an adjacent one of the plurality of first steam generator tubes.
In accordance with a further feature of the invention, the separate outlet tube is bent such that it can be guided past one of the plurality of second steam generator tubes.
In accordance with the invention, the essential structural elements of the suspension of the combustion chamber rear wall are steam generator tubes through which the flow medium flows and which thus perform a double function. In this case, a part stream of the flow medium flows through the supporting tubes, the part stream being supplied back to the main stream of the flow medium on the other side of the supporting structure in the flow direction.
According to a preferred embodiment, the supporting tubes are distributed uniformly over the extent of the width of the combustion chamber rear wall. Only some, substantially less than half, of the steam generator tubes forming the combustion chamber rear wall are required for the supporting function according to the invention.
According to a further embodiment of the invention, all the steam generator tubes leading to the inclined part region of the combustion chamber rear wall run or open out, below the inclined part region of the combustion chamber rear wall, into the balancing header extending approximately horizontally or that side of the rear wall which faces away from the combustion chamber. However, the steam generator tubes used according to the invention as supporting tubes are flow-connected to the balancing header only by pressure-equalizing tubes. This balancing header, by virtue of a pressure balancing, causes a uniform flow distribution within the combustion chamber rear wall as well as in the tubes of the upper inclined part region. Moreover, a partial balancing of the enthalpy of the flow medium flowing into the balancing header takes place therein. This enthalpy balancing has a favorable effect on the temperature distribution in the inclined heating surface located downstream in the direction of flow and forming the lower flank of the nose according to the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in continuous flow steam generator having a double-flue construction, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.